The present invention relates to disk drives and, more particularly, to laminated actuator assemblies made from composite materials and the method for making such actuator assemblies.
Disk drives typically write data to or read data from some type of circular media, such as a magnetic or optical disk. The disk is usually arranged in concentric circles or tracks on the disk. As the disk rotates about a shaft, data is read from or written to the disk by operation of a read/write element or head assembly. An actuator assembly, including an actuator arm, positions the read/write element over the various tracks for purposes of reading data from or writing data to designated tracks on the disk.
It is a continuous goal of the disk drive industry to reduce the size and weight of disk drives while simultaneously increasing, or at least maintaining, storage capacity. With reduced size and increased capacity, disk drives can be used in an ever increasing variety of applications. For example, miniature disk drives not only allow for building smaller portable computers, but also provide enhanced functionality to personal electronic devices (PEDs) such as cameras, music players, voice recorders, cam corders, portable music recorders and other similar devices. In this regard, many disk drive components, like actuator assemblies, are being designed as plastic pieces to reduce weight and cost of production compared to metal actuator assemblies. However, plastic actuator assemblies are more susceptible to breakage from shock or extreme temperature variations that come with use in portable instruments. Moreover, plastic actuator assemblies also are less rigid and therefore susceptible to vibration and bending which can result in positioning errors which may lead to track encroachment. Lack of stiffness or rigidity can also create resonant frequency problems and, as a result, require limitations in the bandwidth of servo systems in which they operate to avoid such problems.
Plastic actuator assemblies are also susceptible to imprecision in molding processes. For example, while filled plastics may have improved properties, they also may have irregularities, such as anisotropic properties, which are difficult to control. Similarly, metal actuators are also susceptible to imprecision in manufacture, whether it be forging, etching or stamping. Such imprecision, even within acceptable tolerances ranges, may create problems in positioning the head assembly relative to the disk. Attaining desired degrees of precision in the manufacture of actuator assemblies is made even more difficult as actuator assemblies become smaller and smaller. Controlling manufacturing tolerances at increasingly smaller sizes in molding, forging, etching or stamping even if attainable, becomes prohibitively expensive.
One embodiment of the present invention is a laminated actuator assembly comprising three or more planar elements, with most of those planar elements comprising carbon fiber composite material made of several layers. These multi-layer carbon fiber composite planar elements are separated by a central planar element comprising a flexure and spacer. The number of individual layers or plies comprising the planar elements may vary. Fiber orientation among the various carbon fiber layers is selectively and strategically placed through the thickness of the carbon fiber planar element to align with principal axes of the beam elements of the actuator arm in order to optimize particular objectives, such as bending and twisting stiffness.
One of the planar elements also comprises a flexure member. The flexure member allows the forward portion of the actuator assembly to pivot relative to the rear portion of the actuator assembly, allowing an optical pick up unit disposed on the distal end of the actuator assembly to move relative to the surface of an optical disk for purposes of maintaining focus on the information layer of the disk. The flexure member is preferably made from a lightweight, flexible metal having a high yield strength and can be formed from either an etching, stamping or die cutting process. The flexure member may be positioned adjacent the outer surface of a carbon fiber planar element, or it may be positioned between two carbon fiber planar elements. In those instances when the flexure member is disposed between carbon fiber planar elements, a spacer also may be included to maintain appropriate spacing between carbon fiber planar elements directly separated by the flexure. The spacer provides for a more uniform adhesive layer in the completed laminated actuator assembly. The flexure member footprint does not necessarily have to match the footprint of the carbon fiber planar elements. Similarly the footprints of the carbon fiber planar elements may vary. Such variability facilitates attachment of other components, such as the optical pickup unit and flex circuit.
The fibers in the various layers of the planar elements need not be carbon but may be glass or light metals such as boron, magnesium or beryllium, or other materials such as kevlar or ceramic. Alternatively, the fibers in any particular layer may comprise a combination of two or more of these materials. The spacer may be made of the same material as the flexure member, or may be made of a laminate of fiber layers such as carbon or of other lightweight materials, such as magnesium, foam core, plastic or honeycomb. The combination provides a structure which is strong, light weight and resistant to bending, vibration and twisting, and one which is ideal for use in a miniaturized environment.
The fiber laminate planar elements provide the structural characteristics of the actuator assembly. These planar elements, or upper and lower composite planar elements when viewed relative to the surface of the disk, are manufactured in arrays of multiple component pieces. More specifically, a number of layers of fiber material are combined to form a composite planar element panel. A water jet or other appropriate cutting device, under computer control, cuts the composite planar element panel into an array of multiple copies of the upper and lower fiber planar elements, still attached to the exterior frame of the overall lamination panel. For efficiency and handling, the component pieces remain attached to the overall lamination panel in an array format. In addition, registration points are also formed in each panel for subsequent use in aligning the panel to the corresponding arrays of components in mating panels during subsequent processing. The panels of flexure elements include similar registration features for co-alignment with the panels of upper and lower carbon fiber planar elements.
As an alternative, unique or individual cuts may be initially made in the composite planar element panels before lamination and all cuts common to the planar elements made following the lamination of the planar elements. Using appropriate registration features, the individual composite planar element panels are laminated to create the laminated actuator assembly panels. Fabrication in this manner provides the option to have different footprint geometries of the individual planar elements or the overall laminate of the actuator assembly, since the component shape can be unique in each planar element.
The number of planar elements in the laminated actuator assembly could range from one, with the flexure on either the top or bottom surface, to as many as two dozen, with the flexure being located on either surface or between any two interior planar elements. The number of fiber layers in a single composite planar element is determined by the thickness limitations of the planar element, dividing the allowable planar element thickness by the fiber diameter at maximum material condition. Practical embodiments would likely range from one to seven planar elements in an actuator assembly. Each planar element can be optimized for directional stiffness properties via fiber orientation, based upon the final placement within the thickness of the planar element and the laminated actuator assembly.
Lamination is accomplished by aligning and bonding multiple fiber layers to form fiber planar elements, and by aligning and bonding one or more fiber planar elements to the flexure planar element. As previously stated, a spacer element may be positioned in a coplanar relationship with the flexure planar element. The bonding process may be accomplished by oven cure or room temperature cure. Pressure is applied to the stack of planar elements during the cure process, via a clamping fixture that can be set to establish a finished laminate stack thickness. Setting of the stack height effectively defines the bond line thickness dimensions so that bond strength and adhesive squeeze out can be optimized. Adhesive is applied to the fiber planar elements either prior to alignment and installation in the clamping fixture or as the arrays of planar elements are placed in the clamping fixture. Adhesive can be applied using silk screen techniques, with the silk screen also having registration members for accurate alignment with the fiber planar elements. Alternatively, the adhesive may be applied by roller or by spraying or other printing or as a film. The clamping fixture may also include a vacuum chuck to constrain movement and maintain alignment of the planar elements and silk screen pattern. The clamping fixture includes complementary registration features which interact with the registration features in the fiber and flexure planar element panels to accurately position the planar elements relative to each other.
In embodiments that utilize a flexure which does not match the footprint of the mating fiber planar elements, and in which a spacer layer is not utilized, a varying bond line thickness is created. In order to prevent adhesive overflow at the edges of the planar elements, the adhesive cannot be applied in a single, uniformly thick layer. To overcome this problem, the adhesive is applied in a single application of discreet stripes of adhesive, analogous to half tone printing procedures. In the areas where the flexure is present, fewer or less dense stripes of adhesives are applied. As a result, when the planar elements are all aligned and appropriate pressure is applied, the adhesive spreads out and uniformly fills the space between the planar elements that encapsulate the flexure member.
Once arrays of upper and lower fiber planar elements and flexure planar elements have been laminated into an array of actuator arms, the arms may be removed (singulated) from the laminated panel for further assembly operations, or left in the panel and further assembly operations performed in panelized, batch process operations.